Heretofore, transparent rubber-modified copolymer resins were employed in various applications including household electric products, packaging materials and optical applications. However, they were inadequate in transparency, impact resistance and rigidity, and they had dependency of the transparency on molding conditions. Thus, they were not satisfactory. Further, they were not adequate against a demand in recent market place for high practical strength.
For example, JP-A-4-180907 discloses a rubber-modified copolymer resin having the toluene-insoluble content, the swelling index, etc. adjusted within certain specific ranges, but for such a resin, it was required to use a specific styrene/butadiene copolymer or a specific reactor, and there was a problem such that the balance of the transparency, the impact resistance, the rigidity, etc. was not sufficient.
JP-A-8-269142 discloses a rubber-modified styrenic resin composition wherein a copolymer of a styrenic monomer and a (meth)acrylic ester monomer, constitutes a continuous phase, and rubber particles having two peaks constitute a dispersed phase, but its use was limited due to the facts that control of the rubber particle size distribution, the gel content, the swelling index, etc. was not sufficient, the dependency of the transparency on the molding conditions was large, and the practical strength was low.
JP-A-11-147993 discloses a rubber-modified styrenic resin composition wherein a copolymer of a styrenic monomer and a (meth)acrylic ester monomer constitutes a continuous phase and rubber particles having two peaks constitute a dispersed phase, and its molecular weight distribution is adjusted to be within a specific range. However, there was a problem that there were many particles having small particle diameters and low impact resistance, and the balance of the impact resistance and the rigidity was not sufficient.
It is an object of the present invention to provide a rubber-modified copolymer resin is excellent in transparency, impact resistance and rigidity and which has little dependency of the transparency on molding conditions, and a rubber-modified copolymer resin composition which has the above-mentioned characteristics and which further has excellent practical strength.